| Summary: | Lack of instrument sensitivity to low electron density (<i>N<sub>e</sub></i>) concentration makes it difficult to measure sharp <i>N<sub>e</sub></i> vertical gradients (four orders of magnitude over 30 km) in the <i>D/E</i>-region. A robust algorithm is developed to retrieve global <i>D/E</i>-region <i>N<sub>e</sub></i> from the high-rate GNSS radio occultation (RO) data, to improve spatiotemporal coverage using recent SmallSat/CubeSat constellations. The new algorithm removes <i>F</i>-region contributions in the RO excess phase profile by fitting a linear function to the data below the <i>D</i>-region. The new GNSS-RO observations reveal many interesting features in the diurnal, seasonal, solar-cycle, and magnetic-field-dependent variations in the <i>N<sub>e</sub></i> morphology. While the <i>D/E</i>-region <i>N<sub>e</sub></i> is a function of solar zenith angle (χ), it exhibits strong latitudinal variations for the same χ with a distribution asymmetric about noon. In addition, large longitudinal variations are observed along the same magnetic field pitch angle. The summer midlatitude <i>N<sub>e</sub></i> and sporadic <i>E</i> (<i>E<sub>s</sub></i>) show a distribution similar to each other. The distribution of auroral electron precipitation correlates better with the pitch angle from the magnetosphere than from one at 100 km. Finally, a new <i>TEC</i> retrieval technique is developed for the high-rate RO data with a top reaching at least 120 km. For better characterization of the <i>E</i>- to <i>F</i>-transition in <i>N<sub>e</sub></i> and more accurate <i>TEC</i> retrievals, it is recommended to have all GNSS-RO acquisition routinely up to 220 km.
|
|---|